By the time the Olympic Games arrive, purpose should be clear: Draw from your training; perform at your best; leave satisfied that all the sacrifice was worth it.

Yet four years ago in Beijing, Brendan Hansen was swimming in his second Olympics — and had no idea why.

“I’m looking at the other end of the pool in the final of the 100 breaststroke and going, ‘Am I really still doing this?’ ” Hansen said. “Am I really still swimming? Still? At 27?”

The athletes who gather this week in Omaha for the U.S. Olympic swimming trials may talk about training methods and tapers, nutrition and nerves. But in their most honest moments, they talk, too, about the forces that ate at Hansen for so long. At some point long ago, each of these women and men jumped into a pool for the first time as girls and boys to have fun, kids splashing about. And at some point, after having devoted so much of their lives to swimming, many of them want nothing more to do with it.

Take Hansen, in 2008, after Beijing.

“I wanted to get as far away from the pool as possible,” he said. “I felt like I had been cheated. I felt like I worked really hard and never saw the benefits of it.”

Hansen turns 31 this summer, and in pools from Omaha to London, where the Olympics begin next month, there will be tears of joy and heartbreak. Yet the tidy interpretations of those emotions — of overwhelming satisfaction from a victory, crippling devastation from a defeat — don’t begin to explain the complicated relationships many athletes have with their sports.

Swimmers are only a subset, Hansen maybe this year’s best example. They have given so much, with no guarantees as to what they’ll get back. They endure early-morning workouts, miss weddings and birthday parties, delay marriages and parenthood, hit the pause button on the rest of their lives for years — and for what?

After the 2008 Olympics, Hansen walked out.

“Those things add up after a while, and you’re like, ‘Dude, life is passing me by while I’m staring at a black line on the bottom of the pool,’ ” Hansen said. “That just didn’t feel right anymore.”

Yet here he is, trying to make his third Olympic team, the sport of swimming front and center in his life again. Yes, he took two years completely off. Yes, he became a triathlete. Yes, he worked for a start-up company, a regular job. And yes, he got married. But the pull of the pool, for someone who had known nothing else for two decades, somehow sucked him in again.

“Whatever’s going on in my life, I feel like if I swim,” Hansen said, “I can kind of center myself and be at my best.”

Centering himself means something different from what it once did, because Hansen's career, to this point, is defined by a lack of return on his investments. He set world records in the 100- and 200-meter breaststrokes at the 2004 Olympic trials. Given that precedent, his performance at the Athens Games — silver in the 100, bronze in the 200, with slower times in each event, and a gold in the medley relay — was viewed in some corners as a failure.

There was even an infuriating wrinkle: Most members of the American team believed Hansen’s chief rival, Japan’s Kosuke Kitajima, used an illegal kick to beat him in the 100.

Either way, that failure — or that perception of failure — fueled Hansen into 2008. “I felt like I got robbed in 2004,” he said, “so I need to come back and make this huge appearance.”

It didn’t work. In the 200 breaststroke at trials, Hansen swam slowly. He was overtaken in the final 25 meters. He didn’t make the team in his best event.

“I’m not sure I still know what happened in that event,” said Eddie Reese, Hansen’s coach at the University of Texas, his coach in 2004 and ’08, his coach now. “Once the gun goes off, a lot of things go through their minds.”

But what about before the gun goes off? Not just seconds prior, but days and weeks and months? This is a topic of discussion for swimmers in those weary moments before the sun rises, or on the weekends given up to their sport, traveling the world but seeing little more than hotel rooms and competition venues.

Then, the big-picture questions — the ones that can leave one of the best swimmers in the world standing on a starting block wondering why he’s still there — creep in.

“He got so caught up in all of it,” said Hansen’s wife, Martha, “he forgot why he swam in the first place.”

‘Why do you play sports?’

This experience is not unique to Hansen. Aaron Peirsol, perhaps the best backstroker in history, trained with Hansen at Texas. For years, including twice at the Olympics, Peirsol led off the best U.S. medley relay team, touched the wall, and Hansen dove in for the second leg. Twice they won gold together. They know all too well the why-do-we-do-this discussions.

“Where, along the way, did you lose the reason you wanted to do your sport to begin with?” Peirsol said. “We talk about it all the time. When you’re a kid, why do you play sports? So you can fall down and get back up. Get tough, get dirty, and play, and you enjoy the process of learning and not being judged and standing back up and doing it again. Then there’s junior Olympics, or school, or Olympic medals that become the goals, and they can detract from the whole reason you began to do it to begin with. . . .

“Everyone’s told that hard work pays off. Not really. If you really like it, you’ll work hard. But if you don’t like it, and you’re being told to work hard, you’re not going to like it. You’re going to resent it.”

This, from a swimmer who won five gold medals and two silvers in his three Olympics, who still owns the world records in the 100- and 200-meter backstrokes, who is younger than Hansen — and who retired even though he could have been a factor in London.

“I stopped because I stopped, man,” Peirsol said. “I’m done.”

Unlike Hansen, Peirsol continued to swim after the 2008 Games. He had a spectacular 2009 season, and seemed headed toward a fourth Olympics.

But at the 2010 U.S. Nationals in Irvine, Calif., he finished second in the 100 backstroke to an upstart, David Plummer. Reese, who also coached Peirsol at Texas and through his pro career, asked him afterward: “What did you feel before that race?”

“I was emotionally flat,” Peirsol told Reese. “I’ve never felt that way before a race before.”

His relationship with swimming had changed. The following February, despite the fact that he had earned the right to swim that summer in the world championships in Shanghai, he left. Unlike Hansen, he filed retirement papers.

“I thought I was grown up,” said Peirsol, who turns 29 next month. “I got awayfrom swimming, and I realized I had some growing up to do.”

But even when it’s pulled off at the right time, a departure can leave a void. Peirsol will be back at the Olympics this summer, sitting in the stands.

“It’ll be emotional for me,” he said, “just because it meant so much to me.”

‘Is this a stupid idea?’

Late in 2010, just as he passed two years without swimming, Hansen started thinking about what he had left behind, about what was left undone. Even with his two gold medals from the medley relays in ’04 and ’08, the Olympics had been wholly unsatisfying.

Martha, a former Texas swimmer whom Hansen had dated since college and who he married in May 2010, asked him, simply: “Are you going to regret this when you’re 40 years old?”

“Yeah, probably,” Hansen replied.

“Well, I don’t want to live with that guy,” Martha said, according to Brendan. “So get your ass in the water.”

Thus, on Jan. 7, 2011 — a date clearly stamped in his mind — Hansen scheduled a lunch with Reese. His first question: “Is this a stupid idea?” Reese looked at his student, fitter than he had ever been, refreshed in a way he had never been.

“It was an easy, ‘Yes,’ to let him do it,” Reese said.

They made a deal that Hansen would quietly begin training with the Texas team, and the two would have another conversation in a month. That second discussion was not necessary.

Hansen swam fast when he got in the pool. He has gotten faster still. And he has done so, those around him said, on his own terms. The questions he posed in his own mind, on that starting block in Beijing, are gone.

“He’s back because he wants to be back,” Peirsol said. “He came back with the idea that, if it works, it works. The irony is that he’ll probably end up doing better with that idea than, ‘I sure as hell better win.’ ”

He will be in the pool Monday in Omaha, in the same arena which brought him so much misery four years ago, for the 100 breaststroke. He believes it will feel like a different place because his attitude is so different.

“I almost feel like he’s younger now than he was in 2008,” Martha Hansen said. “He has a more juvenile spirit now, a healthier outlook.”

What that will yield, he does not know. He hasn’t matched the 2012 times put up by Eric Shanteau, who owns the American records in both breaststroke events, marks Hansen once held. He believes that does not matter.

“I’m really going to kind of stop and enjoy the roses and really enjoy the experience and whatever the outcome is, because I honestly believe that this is all just a dream for me,” Hansen said. “And I’m just going to enjoy the journey, and whatever the outcome is, I’ll deal with that at the end. . . . I’ll just be glad I gave it a try.”

Just giving it a try: It is a child’s thought, a kid’s motivation. And it is a most novel approach at swimming’s highest level.

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